With each generation, wireless communication systems are characterized by ever-higher data rates. While some increase in data rates may be attributed to improvements in modulation, coding, and the like, significant increases in data rates generally require higher system bandwidths. For example, the International Mobile Telecommunications, IMT, advanced (a proposed fourth generation (4G) wireless communication system), mentions bandwidths up to 100 MHz. However, the radio spectrum is a limited resource, and since many operators and systems compete for limited radio resources, it is unlikely that 100 MHz of contiguous spectrum will be free for such systems.
One approach to increasing bandwidth requirements in limited, fragmented spectrum is to aggregate non-contiguous spectrum. From a baseband point of view, this can effectively increase the system bandwidth sufficiently to support up to 1 Gb/s, a throughput requirement for 4G systems. Transmitting data in non-contiguous parts of the spectrum also introduces flexibility, as spectrum utilization may be adapted to existing spectrum use and geographical position. Additionally, different modulation and coding schemes may be advantageously applied to different portions of the spectrum.
A possible evolution of current cellular systems, such as the 3GPP Long Term Evolution (LTE), to support non-contiguous spectrum is to introduce multiple component carriers or multiple channels. In such a multi-channel or multiple component carrier system, each separate portion of spectrum may be considered an LTE system. Multi-channel transmission is likely to be a principal part of the further releases of 3G LTE targeting ITU IMT-Advanced capabilities. A mobile terminal for use in such a system will be capable of receiving multiple component carriers, of different bandwidths, and transmitted at different carrier frequencies. Also High-Speed Packet Access (HSPA) systems can use multiple bands, e.g. dual carrier (downlink) and dual cell (uplink). In the following, the general term “multiple system carrier” is used.
US 2007/007090 discloses a multi-carrier communication system in which radio resources are distributed between a plurality of access terminals. The carriers assigned to an access terminal are determined by the network based on scheduling information received from the access terminal. The scheduling information may include data requirements, Quality-of-Service requirements, available transmit power headroom, the location of the access terminal, or hardware constraints associated with the access terminal. This disclosure does not relate to the use of non-contiguous bandwidths.
The design of a mobile terminal supporting multiple non-contiguous system carriers is a non trivial task. The aggregated spectrum approach implies that the radio receiver architecture for such a mobile terminal will become more complicated than a terminal only capable to receive contiguous system bandwidths. One reason for this is that the front end radio needs to be able to suppress blocking signal in between the spectrum “chunks”. Different kinds of radio architecture can be used for handling this problem; however, they typically have drawbacks compared to standard contiguous system receivers in terms of current consumption. Therefore there is a need for an efficient non-contiguous multi-carrier system design taking into account the challenges in the mobile terminal front end receiver design.